Vertical transistors offer the advantages of greater density across a wafer than do lateral designs such as conventional field effect transistors. One such vertical transistor device is the permeable base transistor (PBT) described in U.S. Pat. No. 4,378,629 to Bozler et al. In that transistor, a metal base layer is sandwiched between single crystal emitter and collector regions. The base layer has openings therein which may be provided by forming the base as a grating. With sufficiently narrow openings in the grating, the metal semiconductor Schottky barrier provides for barrier-limited current flow.
Numerous applications exist for a transistor capable of providing amplification and power generation at EHF frequencies. Sufficiently fast two-terminal devices are presently available, but there is a need for three-terminal devices which provide greater isolation of input and output signals in an analog circuit. The high gain and power added efficiency of the PBT at frequencies in the order of 20 GHz makes it particularly suited to high frequency power applications. The present invention relates to an improved design which particularly adapts the permeable base transistor and other vertical transistors, such as the heterojunction bipolar transistor and vertical field effect transistor, to power applications.